1. Section 1: Units and Measurements
Chemists use an internationally recognized system of units to communicate their findings. K
What I Know W
What I Want to Find Out L
What I Learned

2. Essential Questions
What are the SI base units for time, length, mass, and temperature?
How does adding a prefix change a unit?
How are the derived units different for volume and density?
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Units and Measurements

3. Vocabulary Review New mass base unit second meter kilogram kelvin
derived unit
liter
density
Units and Measurements
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4. Units
Système Internationale d'Unités (SI) is an internationally agreed upon system of measurements.
A base unit is a defined unit in a system of measurement that is based on an object or event in the physical world, and is independent of other units.
To better describe the range of possible measurements, scientists add prefixes to the base units.
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Units and Measurements

5. Add link to concepts in motion interactive table from page 33 here.
Interactive Table – SI Prefixes
Concepts in Motion
FPO
Add link to concepts in motion interactive table from page 33 here.
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Units and Measurements

6. Base Units and SI Prefixes
The SI base unit of time is the second (s), based on the frequency of radiation given off by a cesium-133 atom.
The SI base unit for length is the meter (m), the distance light travels in a vacuum in 1/299,792,458th of a second.
The SI base unit of mass is the kilogram (kg), about 2.2 pounds.
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Units and Measurements

7. Base Units and SI Prefixes
The SI base unit of temperature is the kelvin (K).
Zero kelvin is the point where there is virtually no particle motion or kinetic energy, also known as absolute zero.
Two other temperature scales are Celsius and Fahrenheit.
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Units and Measurements

8. Derived Units Not all quantities can be measured with SI base units.
A unit that is defined by a combination of base units is called a derived unit.
Example: The SI unit for speed is meters per second (m/s).
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Units and Measurements

9. Derived Units
Another quantity that is measured in derived units is volume (cm3), measured in cubic meters. The three cubes show volume relationships between cubic meters (m3), cubic decimeters (dm3), cubic centimeters (cm3), and cubic millimeters (mm3).
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Units and Measurements

10. Derived Units
Volume is measured in cubic meters (m3), but this is very large. A liter (L) is equal to one cubic decimeter (dm3), that is, 1 L equals 1 dm3.
Density is a derived unit, g/cm3, the amount of mass per unit volume. The density of a substance usually cannot be measured directly. You can calculate density using the following equation:
density = mass/volume
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Units and Measurements

11. USING DENSITY AND VOLUME TO FIND MASS
KNOWN
UNKNOWN
density = 2.7 g/mL
mass = ? g
initial volume = 10.5 mL
final volume = 13.5 mL
Use with Example Problem 1.
Problem
When a piece of aluminum is placed in a 25-mL graduated cylinder that contains mL of water, the water level rises to mL. What is the mass of the aluminum?
SOLVE FOR THE UNKNOWN
State the equation for volume.
volume of sample = final volume - initial volume
Substitute final volume = 13.5 mL and initial volume = 10.5 mL.
volume of sample = 13.5 mL mL
volume of sample = 3.0 mL
State the equation for density.
Response
ANALYZE THE PROBLEM
The mass of aluminum is unknown. The known values include the initial and final volumes and the density of aluminum. The volume of the sample equals the volume of water displaced in the graduated cylinder. The density of aluminum is 2.7 g/mL. Use the density equation to solve for the mass of the aluminum sample.
Units and Measurements
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12. USING DENSITY AND VOLUME TO FIND MASS
EVALUATE THE ANSWER
Check your answer by using it to calculate the density of aluminum.
Because the calculated density for aluminum is correct, the mass value must also be correct.
SOLVE FOR THE UNKNOWN
Solve the equation for mass.
mass = volume × density
Substitute volume = 3.0 mL and density = 2.7 g/mL.
mass = 3.0 mL × 2.7 g/mL
Multiple, and cancel units.
mass = 3.0 mL × 2.7 g/mL = 8.1 g
Units and Measurements
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13. Review Essential Questions Vocabulary
What are the SI base units for time, length, mass, and temperature?
How does adding a prefix change a unit?
How are the derived units different for volume and density?
Vocabulary
base unit
second
meter
kilogram
kelvin
derived unit
liter
density
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Units and Measurements